The invention relates to a face seal device for sealing a shaft with respect to a casing and more particularly to a face seal device including a mounting aid which simplifies the mounting of the face seal device on a shaft. A known face seal device of this type (DE-A-3318296) has a mounting aid in the form of a sleeve upon the outer periphery of which a seal ring held on a mounting gland and representing the non-rotational seal ring of a pair of co-operating seal rings is disposed. Furthermore, the mounting gland acts as a carrier for diverse auxiliary means such as a biasing means and a secondary sealing means. The sleeve, together with the seal ring and the mounting gland, can be pushed onto the shaft and be withdrawn from the seal ring after fixing the mounting gland to the casing. Furthermore, the rotating seal ring can be seated on the end of the sleeve using a frictional seating, whereby this seal ring will attain its final operational alignment relative to the non-rotational seal ring only when caused to engage the shaft, but not prior thereto by means of the sleeve. Thus, in the first place, the sleeve is but a mounting aid for less skilled personnel. Automatic assembly of the face seal device in the course of an apparatus production line process cannot be contrived. Furthermore, a face seal device in the form of a unit ready for assembly is known (EP-A-1024319). This face seal device does not comprise a mounting aid and while being suitable for use in an apparatus production line process, has a complicated construction and is therefore expensive to manufacture.